The manufacture of insulating products based on mineral wool generally comprises a stage of manufacture of the wool itself, which can be carried out by various processes, for example according to the known technique of fiberizing by external or internal centrifugation. Internal centrifugation consists in introducing the molten mineral material (glass or rock) into a centrifugal device comprising a multitude of small orifices, the material being projected toward the peripheral wall of the device under the action of the centrifugal force and escaping therefrom in the form of filaments. On leaving the centrifugal device, the filaments are drawn and carried towards a receiving member by a gas stream having a high temperature and a high speed, in order to form there a web of fibres (or mineral wool).
In order to provide for the assembly of the fibres together and to make it possible for the web to have cohesion, a sizing composition comprising a thermosetting resin is projected onto the fibres, on the route between the outlet of the centrifugal device and the receiving member. The web of fibres coated with the size is subjected to a heat treatment, at a temperature generally of greater than 100° C., in order to bring about the polycondensation of the resin and to thus obtain a thermal and/or acoustic insulating product having specific properties, in particular dimensional stability, tensile strength, thickness recovery after compression and homogeneous colour.
The sizing composition to be projected onto the mineral wool is generally provided in the form of an aqueous solution including the thermosetting resin and additives, such as a catalyst for the crosslinking of the resin, an adhesion-promoting silane, a dust-preventing mineral oil, and the like. The sizing composition is generally applied to the fibres by spraying.
The properties of the sizing composition depend largely on the characteristics of the resin. From the viewpoint of the application, it is necessary for the sizing composition to exhibit good sprayability and to be able to be deposited at the surface of the fibres in order to efficiently bind them.
The resin has to be stable for a given period of time before being used to form the sizing composition, which composition is generally prepared at the time of use by mixing the resin and the additives mentioned above.
At the regulatory level, it is necessary for the resin to be regarded as non-polluting, that is to say for it to comprise—and for it to generate during the sizing stage or subsequently—as little as possible in the way of compounds which may be harmful to human health or to the environment.
The thermosetting resins most commonly used are phenolic resins belonging to the family of the resols. In addition to their good crosslinkability under the abovementioned thermal conditions, these resins are soluble in water, have a good affinity for mineral fibres, in particular glass fibres, and are relatively inexpensive.
Resols are generally obtained by reaction of a phenol and an aldehyde under basic conditions, a proportion of these compounds which have not reacted occurring in the final resin. The most widely used aldehyde is formaldehyde, the presence of which in the form of free formaldehyde is undesirable because of its known harmful effects.
Regulations with regard to environmental protection, which are becoming more restrictive, are forcing manufacturers of insulating products to look for solutions which make it possible to further lower the levels of undesirable emissions, in particular of formaldehyde, whether with regard to the manufacture of the insulating products or the use thereof.
Solutions in which resols are replaced in sizing compositions are known and are based on the use of a carboxylic acid polymer, in particular an acrylic acid polymer, and of a hydroxylated compound.
In U.S. Pat. No. 5,340,868, the size comprises a polycarboxylic polymer, a β-hydroxyamide and an at least trifunctional monomeric carboxylic acid.
Sizing compositions are also known which comprise a polycarboxylic polymer, a polyol and a catalyst, which catalyst is a catalyst comprising phosphorus (U.S. Pat. No. 5,318,990, U.S. Pat. No. 5,661,213, U.S. Pat. No. 6,331,350, US 2003/0008978), a fluoroborate (U.S. Pat. No. 5,977,232) or else a cyanamide, a dicyanamide or a cyanoguanidine (U.S. Pat. No. 5,932,689).
Sizing compositions are also known which comprise an alkanolamine including at least two hydroxyl groups and a polycarboxylic polymer (U.S. Pat. No. 6,071,994, U.S. Pat. No. 6,099,773, U.S. Pat. No. 6,146,746, US 2002/0091185) in combination with a copolymer (U.S. Pat. No. 6,299,936).
The sizing compositions based on a polycarboxylic polymer and on a polyol can additionally include a cationic, amphoteric or nonionic surfactant (US 2002/0188055) or a coupling agent of silane type (US 2004/0002567).
The proposal has also been made to replace all or part of the hydroxylated compound by a saccharide.
A description is given, in US 2005/0215153, of a size formed from a prebinder comprising polymer of carboxylic acid and of a polyol, and from a dextrin as cobinder.
Furthermore, an adhesive composition based on heat-crosslinkable polysaccharides is known which can be used as size for mineral wool (U.S. Pat. No. 5,895,804). The composition comprises a polycarboxylic polymer having at least two carboxylic acid functional groups and a molecular weight of at least equal to 1000, and a polysaccharide having a molecular weight of at least equal to 10 000.
A formaldehyde-free aqueous sizing composition is also known which comprises a Maillard reaction product, in particular combining a reducing sugar, a carboxylic acid and aqueous ammonia (WO 2007/014236). In WO 2009/019232 and WO 2009/019235, the proposal is made to replace the carboxylic acid with an acid precursor derived from an inorganic salt, in particular an ammonium salt, which exhibits the additional advantage of being able to replace all or part of the aqueous ammonia.
In WO 2009/080938, the sizing composition for mineral wool comprises a monosaccharide and/or a polysaccharide and an organic polycarboxylic acid with a molar mass of less than 1000, optionally in combination with a catalyst which makes it possible to adjust the crosslinking start temperature.
Furthermore, provision is made, in WO 2011/045531, for a sizing composition for mineral wool based on a reducing sugar and on an inorganic acid metal salt chosen from inorganic acid alkali metal, alkaline earth metal, transition metal or poor metal salts.